During arthroscopic surgery, a small incision is made in the skin covering the arthroscopic site or joint so that surgical instruments may be placed in the joint and manipulated through arthroscopic visualization. The surgical instruments can be used to perform various tasks, such as forming a recipient site socket (e.g., a femoral or tibial bone tunnel) for receiving a soft tissue graft during reconstructive surgery.
For example, in a typical trans-tibial arthroscopic ACL procedure, a drill is used to form recipient site sockets in the tibia and the femur. The drill is first used to form a tunnel through the tibia, starting at the anterior surface of the tibia and advancing inward towards the knee joint. The resulting tibial tunnel provides access to the femur for drilling a femoral tunnel, starting within the joint space and advancing towards the exterior of the femur. Drilling of the femoral tunnel ceases when the desired depth is reached, such that the resulting femoral tunnel is a blind hole, with only a small guide wire sized hole extending all the way through to the exterior of the femur. In this trans-tibial approach, the femoral tunnel is more or less straight up and down, which is biomechanically suboptimal and reduces the rotational stability of the joint.
One way to improve joint biomechanics and rotational stability is to instead use an anteromedial portal in the femur. In an anteromedial approach, a drill is inserted through a portal formed in the front of the knee on the medial side into the femoral notch to drill a tunnel in the lateral condyle. The resulting bone tunnel is placed in a more anatomically-correct position. This approach involves several challenges, however, that arise from limitations of existing cutting instruments. For example, the surgeon must be careful when advancing the relatively large-diameter drill to avoid damaging the cartilage of the medial condyle.
An alternative method is to use an outside-in approach with a retro-cutting instrument to form a stepped opening in the femur, as shown in FIG. 1. Initially, a hole having a diameter D1 is drilled, starting at the outside of the femur and advancing inward towards the joint in the direction of the illustrated arrow A1. The drill is then partially withdrawn in the direction of the illustrated arrow A2 with a retro-cutting feature activated to widen a distal portion of the hole to a diameter D2. The retro-cutting feature is then de-activated to allow the drill to be completely withdrawn through the reduced-diameter proximal portion of the hole. There are many other procedures in which it can be desirable to form a stepped opening in a similar manner.
Existing retro-cutting instruments suffer from a number of disadvantages. For example, existing instruments can only retro-cut tunnels of a single diameter. Thus, when a need exists to drill multiple tunnels with different diameters, multiple instruments having different diameters must be used, increasing inventory and sterilization costs as well as surgical complexity.
Furthermore, in existing retro-cutting instruments, the drill tip for forward cutting and the retrograde cutting tip are one in the same. When retrograde cutting is to be performed, the forward cutting tip is simply hinged outward such that it is disposed approximately perpendicular to the main drill shaft. In this position, the open end of the main drill shaft tends to spread open and the tip can break off. Also, since the same structure is used to perform forward drilling and retrograde cutting, the shape of the structure cannot be optimized for one task or the other. This can reduce the instrument's cutting performance and/or increase the risk of the tip being damaged.
Accordingly, a need exists for improved cutting instruments and related methods.